This application claims priority from Japanese Patent Application No. 2002-048641 filed Feb. 25, 2002, which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an ink container, an inkjet printing apparatus utilizing the ink container, and an ink supplying method and, more particularly, the invention is preferably applied to an inkjet printing apparatus in which ink is intermittently supplied to a printing head for ejecting ink.
2. Description of the Related Art
Inkjet printing apparatuses which form an image on a printing medium by depositing ink to the printing medium using an inkjet printing head include that which form an image by ejecting ink while moving a printing head relative to a printing medium and that which form an image by ejecting ink while moving a printing medium relative to a fixed printing head conversely.
There are two general types of methods of supplying ink to a printing head used in such an inkjet printing apparatus. One is a type in which a supply system is configured such that an amount of ink is always or continuously supplied to a printing head according to the amount of ink ejected (hereinafter referred to as a continuous supply type), and the other is a type in which a printing head is provided with a reservoir (sub-tank or second ink tank) for reserving a predetermined amount of ink and in which a supply system is configured such that ink is supplied to the reservoir from an ink supply source (main tank or first ink tank) at appropriate timing or intermittently (hereinafter referred to as an intermittent supply type).
The continuous supply type is further categorized into two types, for example, when it is used in an inkjet printing apparatus of a type referred to as a serial type in which a printing head is scanned back and forth in predetermined directions relative to a printing medium and in which the printing medium is transported in a direction substantially orthogonal thereto to form an image. One is a type referred to as an on-carriage type in which ink is supplied by integrally or detachably attaching an ink tank to a printing head that is carried and moved back and forth (main scanning) by a carriage. The other is a tube supply type in which an ink tank that is separate from a printing head carried on a carriage is fixedly installed in a part of a printing apparatus other than the printing head and in which the ink tank is connected to the printing head through a flexible tube to supply ink. In some of the latter type, a second ink tank that serves as an intermediate tank between an ink tank and a printing head is mounted on the printing head or the carriage.
When an on-carriage type structure is adopted, there are limits on the project area in a direction perpendicular to the main scanning direction and volume of members that move with a carriage (a printing head and an ink tank undetachably or detachably integrated with the same). Therefore, only an ink tank having a very limited capacity can be used when a small-sized printing apparatus, especially, a portable printing apparatus is to be formed. This results in very frequent replacement of the printing head integral with the ink tank or the ink tank alone, which has been problematic from the viewpoint of operability and running cost. Further, the recent spread of so-called mobile apparatus is remarkable and, for example, ultra-compact inkjet printers have been proposed which can be integrated with notebook type personal computers and digital cameras. It is considered impractical to design such printers in adaptation to the on-carriage method.
When a tube supply type structure is adopted, although members that move with a carriage during main scanning can be made compact to some degree, it is difficult to make the apparatus as a whole compact because a space is required for a tube member to move to follow up the carriage, the tube member coupling a printing head on the carriage and an ink tank located outside the carriage to supply ink. Further, the recent trend is that a carriage is scanned at a high speed to accommodate increases in the speed of printing operations, and resultant severe rocking of a tube that follows the carriage results in changes in the pressure of ink in an ink supply system for the printing head. It is therefore required to provide various complicated pressure buffering mechanisms in order to suppress pressure changes, it has been difficult to achieve a size reduction in this respect too.
On the contrary, in the case of the intermittent supply method that is used for serial type inkjet printing apparatus for example, a relatively small second ink tank and printing head are provided on a carriage; a relatively large first ink tank is provided in a part other than the carriage of the printing apparatus; and a supply system is configured such that ink is supplied from the first ink tank to the second ink tank at appropriate timing. A structure is also employed in which the ink supply system between the first and second ink tanks is spatially separated or the ink channel is blocked with a valve during main scanning to achieve fluid isolation between the first and second ink tanks. Basically, this makes it possible to solve various problems attributable to the size of moving members as described above such as an ink tank and the rocking of a tube that have limited efforts to achieve a small size in the case of the continuous supply type.
When an intermittent supply type structure is adopted, however, it is important to adjust the pressure inside a second ink tank properly, because a negative pressure relative to the atmosphere must be generated in order to maintain ink meniscuses formed at ejection openings. While the second ink tank may be located in a position lower than the position of ejection openings of the printing head to generate a negative pressure in the second ink tank naturally, this puts a limit on even the position and attitude or orientation of the ink tank and has resulted in problems including leakage of ink from the ejection openings especially in case that a portable printing apparatus is to be provided which is unstable in attitude or orientation during transportation.
Under such circumstances, proposals have been made including a proposal in which a porous member such as a sponge for holding ink is contained a second ink tank to generate an adequate negative pressure. Such a structure is advantageous even for a portable printing apparatus whose attitude is unstable during transportation. However, the ink containing efficiency of the second ink tank is limited by the negative pressure generating mechanism such as a porous member provided in the second ink tank. Further, designing may be limited with respect to the endurance of the porous member against deposition and deterioration of a dye or pigment in ink, which also reduces freedom in selecting ink.
Further, in such a structure, since the porous member is always over-charged with ink when ink charging is completed, the over-charged ink in the porous member must be discharged as waste ink without fail by performing an operation of sucking the printing head through the ejection openings after the charging is completed in order to apply a required negative pressure to the printing head. That is, a problem arises in that a charging operation is accompanied by the generation of waste ink.
The invention was conceived taking the above-described problems into consideration, and it employs an intermittent supply system as an ink supplying method and provides a structure which does not fundamentally result in waste of ink such as generation of waste ink associated with a charging operation to apply a predetermined negative pressure to a printing head, which achieves high charging efficiency and a short charging time, and which can be easily kept resistant to ink, i.e., a structure with which freedom in selecting ink can be increased.
The invention thus contributes to the structure of a compact and portable inkjet printing apparatus.
In a first aspect of the present invention, there is provided an ink container that can be disposed halfway of an ink supply path connecting a printing head for performing printing by ejecting ink and an ink tank serving as a supply source of ink to be supplied to the printing head, comprising:
an ink containing body capable of containing ink introduced thereto from the ink tank in a state in which it is in fluid communication with the ink tank, the ink containing body supplying the ink contained therein to the printing head during printing and having a part that can be displaced in the direction of increasing an internal volume thereof to introduce the ink;
a housing having an inner space in which a pressure can be adjusted, the housing allowing the ink containing body to be contained in the space and allowing an increase in the internal volume thereof in accordance with the pressure adjustment; and
means provided at the ink containing body for urging the ink containing body in the direction of increasing of the internal volume of the same to generate a negative pressure that is in equilibrium with an ability to hold meniscus formed at an ink ejecting portion of the printing head,
wherein the ink containing body has a flexible structure which expands when the inner space of the housing is depressurized to increase the internal volume and which contracts when the inner space of the housing is pressurized to decrease the internal volume; and the urging means generates the negative pressure when the inner space of the housing is pressurized to decrease the internal volume of the ink containing body after the internal volume of the ink containing body is maximized as a result of depressurization of the inner space of the housing.
In a second aspect of the present invention, there is provided a printing head unit comprising:
a printing head for performing printing by ejecting ink; and
an ink container that can be disposed halfway of an ink supply path connecting the printing head and an ink tank serving as a supply source of ink to be supplied to the printing head, having:
an ink containing body capable of containing ink introduced thereto from the ink tank in a state in which it is in fluid communication with the ink tank, the ink containing body supplying the ink contained therein to the printing head during printing and having a part that can be displaced in the direction of increasing an internal volume thereof to introduce the ink;
a housing having an inner space in which a pressure can be adjusted, the housing allowing the ink containing body to be contained in the space and allowing an increase in the internal volume thereof in accordance with the pressure adjustment; and
means provided at the ink containing body for urging the ink containing body in the direction of increasing of the internal volume of the same to generate a negative pressure that is in equilibrium with an ability to hold meniscus formed at an ink ejecting portion of the printing head,
wherein the ink containing body has a flexible structure which expands when the inner space of the housing is depressurized to increase the internal volume and which contracts when the inner space of the housing is pressurized to decrease the internal volume; and the urging means generates the negative pressure when the inner space of the housing is pressurized to decrease the internal volume of the ink containing body after the internal volume of the ink containing body is maximized as a result of depressurization of the inner space of the housing.
In a third aspect of the present invention, there is provided an inkjet printing apparatus utilizing a printing head for performing printing by ejecting ink, an ink tank serving as a supply source of ink to be supplied to the printing head, and the ink container according to the above first aspect provided halfway of an ink supply path connecting them, comprising:
a channel opening and closing unit for establishing and blocking fluid communication between the ink tank and the ink containing body; and
a pressure regulating unit for reducing the pressure in the inner space of the housing in the communicated state to increase the internal volume of the ink containing body and for increasing the pressure in the inner space of the housing to decrease the internal volume of the ink containing body.
In a fourth aspect of the present invention, there is provided an ink supplying method used for an inkjet printing apparatus utilizing a printing head for performing printing by ejecting ink, an ink tank serving as a supply source of ink to be supplied to the printing head, and the ink container according to the above first aspect provided halfway of an ink supply path connecting them, and used for supplying the ink to the ink container from the ink tank, the method comprising the steps of:
establishing fluid communication between the ink tank and the ink containing body;
reducing the pressure in the inner space of the housing in the communicated state to increase the internal volume of the ink containing body, thereby introducing ink from the ink tank to the ink containing body; and
increasing the pressure in the inner space of the housing in the communicated state to decrease the internal volume of the ink containing body, thereby introducing ink from the ink containing body to the ink tank, a negative pressure being thus generated in the ink containing body in equilibrium with an ability to hold meniscus formed at an ink ejecting portion of the printing head.
In a fifth aspect of the present invention, there is provided a method for supplying ink to an ink container for containing ink to be supplied to a printing head for performing printing by ejecting ink from an ink tank, the ink container accommodating an ink containing body capable of containing the ink therein and capable of generating a negative pressure by an elastic force, the method comprising the steps of:
establishing fluid communication between the ink tank and the ink containing body;
depressurizing the interior of the ink container to expand the ink containing body, thereby introducing the ink to the ink containing body from the ink tank; and
pressurizing the interior of the ink container to contract the ink containing body, thereby introducing ink from the ink containing body to the ink tank, a negative pressure being thus generated in the ink containing body in equilibrium with an ability to hold meniscus formed at an ink ejecting portion of the printing head.
In a sixth aspect of the present invention, there is provided a method for supplying ink to an ink container for containing ink to be supplied to a printing head for performing printing by ejecting ink from an ink tank, the ink container accommodating an ink containing body capable of containing the ink therein and capable of changing an internal volume thereof with a flexible structure, the method comprising the steps of:
establishing fluid communication between the ink tank and the ink containing body;
increasing the internal volume of the ink containing body, thereby introducing the ink to the ink containing body from the ink tank; and
decreasing the internal volume of the ink containing body, thereby introducing ink from the ink containing body to the ink tank, a negative pressure being thus generated in the ink containing body in equilibrium with an ability to hold meniscus formed at an ink ejecting portion of the printing head.
Incidentally, in the present specification, the wording xe2x80x9cprintingxe2x80x9d means not only a condition of forming significant information such as characters and drawings, but also a condition of forming images, designs, patterns and the like on printing medium widely or a condition of processing the printing media, regardless of significance or unmeaning or of being actualized in such manner that a man can be perceptive through visual perception.
Further, the wording xe2x80x9cprinting mediumxe2x80x9d means not only a paper used in a conventional printing apparatus but also everything capable of accepting inks, such as fabrics, plastic films, metal plates, glasses, ceramics, wood and leathers, and in the following, will be also represented by a xe2x80x9csheetxe2x80x9d or simply by xe2x80x9cpaperxe2x80x9d.
Still further, the wording xe2x80x9cinkxe2x80x9d (also referred to as xe2x80x9cliquidxe2x80x9d in some occasions) should be interpreted in a broad sense as well as a definition of the above xe2x80x9cprintingxe2x80x9d and thus the ink, by being applied on the printing media, shall mean a liquid to be used for forming images, designs, patterns and the like, processing the printing medium or processing inks (for example, coagulation or encapsulation of coloring materials in the inks to be applied to the printing media).
Meantime, the present invention may be applied to a printing head in which a thermal energy generated by an electrothermal transducer is utilized to cause a film boiling to liquid in order to form bubbles, a printing head in which an electromechanical transducer is employed to eject liquid, a printing head in which a static electricity or air current is utilized to form and eject a liquid droplet and the others which are proposed in the art of an inkjet printing technology. Specifically, the printing head in which the electrothermal transducer is utilized is advantageously employed to achieve a compact structure.
Still further, the wording xe2x80x9cnozzlexe2x80x9d, as far as not mentioned specifically, represents to an ejection opening, a liquid passage communicated with the opening and an element for generating an energy used for ink, in summary.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.